The present invention relates generally to cleaning surface layers in integrated circuit fabrication, and in particular to the development of cleaning solutions and methods for the removal of abrasive particles and other residuals from integrated circuit surface layers.
Chemical-mechanical planarization (xe2x80x9cCMPxe2x80x9d) processes are frequently used to planarize the surface layers of a wafer or other substrate in the production of ultra-high density integrated circuits. In typical CMP processes, a wafer is pressed against a slurry on a polishing pad under controlled conditions. Slurry solutions generally contain small, abrasive particles that mechanically remove the surface layer of the wafer. Slurry solutions may further contain chemicals that assist the removal process. The polishing pad is generally a planar pad made from a relatively soft, porous material, such as blown polyurethane. The wafer is abraded by the abrasive particles, thereby leveling or planarizing the surface of the wafer. After the wafer is planarized, it is cleaned to remove residual particles on the surface of the wafer that were introduced to the CMP process by the slurry, the polishing pad or the wafer itself. As an alternative to slurry solutions, the abrasive particles may be carried by the pad itself.
CMP processing is particularly useful for planarizing a metallic surface layer used to form conductive features, such as interlayer connectors and/or conducting lines. As an example, these interconnects are often formed by a method known as a dual damascene technique. Using the dual damascene technique, contact vias and conductor trenches are patterned into an insulating layer of a semiconductor wafer and a layer of metal is formed over this structure. This blanket layer of metal fills the vias and trenches and covers the upper surface of the wafer. Excess metal formed on the upper surface of the wafer is then removed by CMP to a level at or below the surface of the insulating layer.
After the excess metal is removed, residual materials from the slurry, polishing pad or wafer remain on the planarized surface of the wafer. The residual materials commonly include particles attracted to the surface of the wafer, such as by electrostatic or mechanical forces, as well as material bonded to the surface of the wafer. Residual materials attracted to the surface of the wafer may include abrasive particles from the slurry and particles of the metal layer removed from the surface of the wafer. Residual materials bonded to the surface of the wafer may include any remaining excess metal not removed during the planarization. To reduce defects in the finished integrated circuit device, it is generally necessary to clean such residual materials from the planarized surface of the wafer prior to further processing.
A common post-CMP cleaning approach is to use a slurry dispersant to first remove the materials attracted to the surface of the wafer. Slurry dispersants may include deionized (DI) water to simply flush such residuals from the surface of the wafer. Mechanical action, such as brush scrubbing or megasonics, may assist the removal of these attracted residuals. The slurry dispersant may also include materials to complex or otherwise bind such residuals to aid in their removal.
After removal of the materials attracted to the surface of the wafer, the wafer is often etched to remove the material bonded to the surface of the wafer. Such residuals generally are unaffected by slurry dispersants. As these residuals are typically remaining patches of the conductor material, their removal is also important to proper device performance.
In these two-step approaches, the appropriate slurry dispersants and etchants are highly dependent upon their respective target residual materials. Often, the slurry dispersants and etchants may be incompatible with each other, thus requiring a cleaning step to remove traces of the slurry dispersant before etching the bonded residuals. Each processing step creates added cost and the opportunity for introducing additional defects into the integrated circuit device.
In the competitive semiconductor industry, it is desirable to maximize the yield of finished wafers. The uniformity of the planarized surface and maximization of yield is, in part, a function of the effectiveness and repeatability of the solutions and processes used for the removal of residuals following CMP. While a wide variety of dispersant and etchant solutions are available, these solutions are generally specific to the composition of the material to be removed. One must also avoid damaging the surrounding materials.
As device sizes continue to decrease, designers must turn to higher-conductivity materials for use in interconnect lines and contacts to replace aluminum and its alloys. Some of these higher-conductivity materials include silver and its alloys.
For the reasons stated above, and for other reasons stated below that will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for alternative solutions and methods for removing planarization residuals in the fabrication of integrated circuit devices, particularly following mechanical removal of a silver-containing layer.
Cleaning solutions and methods for removing residuals from the surface of an integrated circuit device are described herein. Such solutions and methods find particular application in the fabrication of a dual damascene structure following removal of excess portions of a silver-containing metal layer from a device surface. The cleaning solutions and methods facilitate removal of particulate residuals as well as unremoved portions of the metal layer in a single cleaning process. The cleaning solutions are dilute aqueous solutions containing hydrogen peroxide and at least one acidic component and are substantially free of particulate material. Acidic components include carboxylic acids and their salts.
For one embodiment, the invention provides a method of removing residuals from a surface of an integrated circuit device following mechanical removal of a metal layer. The method includes contacting the surface of the integrated circuit device with a clean aqueous solution containing hydrogen peroxide and at least one acidic component selected from the group consisting of carboxylic acids and their salts. For a further embodiment, the carboxylic acids are hydroxy acids.
For another embodiment, the invention provides a method of removing residuals from a surface of an integrated circuit device following mechanical removal of a silver-containing metal layer. The method includes contacting the surface of the integrated circuit device with an acidic aqueous solution consisting essentially of hydrogen peroxide, water and at least one acidic component. Each acidic component is either a carboxylic acid or a salt of a carboxylic acid. For a further embodiment, the carboxylic acids are hydroxy acids.
For yet another embodiment, the invention provides a method of removing residuals from a surface of an integrated circuit device following mechanical removal of a silver-containing metal layer. The method includes contacting the surface of the integrated circuit device with a solution consisting essentially of hydrogen peroxide, water and an ammonium salt of a hydroxy acid. For a further embodiment, the ammonium salt of a hydroxy acid,is an ammonium salt of citric acid.
For one embodiment, the invention provides a method of fabricating an integrated circuit device. The method includes forming a metal layer on a patterned insulating layer, mechanically removing a portion of the metal layer from the surface of the patterned insulating layer, and contacting the surface of the patterned insulating layer with a clean solution, thereby removing at least a portion of any residuals from the surface of the patterned insulating layer. The solution contains hydrogen peroxide, an aqueous solvent and at least one acidic component selected from the group consisting of carboxylic acids and their salts.
For another embodiment, the invention provides a post-planarization cleaning solution. The cleaning solution contains hydrogen peroxide, an aqueous solvent and at least one acidic component selected from the group consisting of carboxylic acids and their salts. For a further embodiment, the salts of the carboxylic acids are ammonium salts of the carboxylic acids. For a still further embodiment, each acidic component is either acetic acid, citric acid, lactic acid, malic acid, an acetate, a citrate, a lactate or a malate.
Further embodiments of the invention include solutions and methods of varying scope.